The present invention relates generally to agricultural spraying implements and more specifically to a hydraulic rate control system for such implements.
Agricultural chemicals such as herbicides, insecticides and fertilizers are often applied in liquid form to soil or crops. A solution of the chemical and a diluting liquid such as water are pumped from a tank through spray nozzles or the like to the soil or the crops being treated. For maximum effectiveness, economy and safety, the rate of application must be carefully controlled. As the speed at which the sprayer is propelled through the field is increased or decreased, the amount of chemical pumped must increase or decrease accordingly to maintain the desired gallons per acre coverage.
At times during the spraying operation, the operator must change the application rate to best suit the particular soil, crop, weed, or insect conditions or the like encountered. Often the rate change cannot be made easily and accurately.
The rate at which the chemical is applied is dependent on the nozzle or tip size and width of the spray pattern per tip, with the number of gallons per acre applied increasing as the tip size is increased or as the width per tip is decreased. A control is necessary which takes into account the tip size and the width per tip, and which utilizes a means for setting the desired gallons per acre coverage based on these factors and which is independent of the ground speed of the spraying implement.
Typical of prior art rate control systems are those in which chemical concentrates from a separate supply tank are injected at a rate proportional to the vehicle's land speed into water which is dispensed at a constant rate. Such a system is shown for example in U.S. Pat. No. 4,005,803 and requires separate tanks for storing the chemical and the dilutant.
Other rate control systems, such as shown in U.S. Pat. Nos. 3,550,854 and 3,670,962, utilize a centrifugal governor driven from a ground wheel to control the flow of liquid from the tank to the discharge nozzles so that the amount of solution applied per acre remains constant regardless of ground speed. Fairly complex and expensive drive, governor, and governor-controlled valve assemblies are required.
Other types of systems have used ground-driven pumps for delivering the chemical to the nozzles at a pressure related to speed so that the gallons per acre sprayed remains essentially constant regardless of speed. However, the high pressure and high capacity requirements of present-day sprayers make such a system impractical since the output is limited, for example by wheel traction. Systems which use electronic regulating means have been devised for regulating sprayer output in proportion to rate of advance, such as that shown in U.S. Pat. No. 4,083,494. Such systems, however, often require variable displacement pumps or electrically operated valves which increase the cost and complexity of the system, and which require connecting the system to a source of electrical power.
Another regulating system described in U.S. Pat. No. 3,784,100 utilizes a selector valve directly in the main flow line to the spray nozzles. The valve divides the flow between the nozzles and a bypass line leading to the inlet of the pump. A ground speed valve is adjusted to correspond to the vehicle ground speed. The device provides a predetermined application rate for a particular vehicle ground speed and crop row spacing, but requires the use of interchangeable valve cores with different sized orifices and the use of a chart for correlating ground speed, crop row spacing, application rate and pressure to determine the required operating pressure which is monitored with a meter. The control valve generally requires readjusting if the ground speed changes, and changing the spray rate requires more than simply dialing in the desired rate on the control. The valve system used directly controls the solution to be sprayed which is common in many of the prior art examples, and therefore the chemical must be piped to the control at the operator's station, usually requiring more plumbing and increasing the danger of subjecting the operator to contact with the chemical if a leak occurs.
In many of the prior art devices in which there is direct contact between the valve and the chemical to be applied corrosion of the control valve is a problem. In addition, the chemical often has a sticky base which will clog the valve and prevent accurate metering. Dirt or sediment in the solution to be sprayed can also cause clogging and result in malfunctioning of the metering system.